The type of deflecting yoke core to which the present invention relates is used to constitute a deflecting yoke. A deflecting yoke, which is constituted by providing a horizontal deflection coil and a vertical deflection coil at a deflecting yoke core, is mounted between a neck and a funnel of a cathode ray tube (CRT). An electron beam emitted from an electron gun provided at the neck is deflected along horizontal and vertical directions. In a standard deflecting yoke core, the shape of an opening end at the neck portion and the shape of an opening end at the funnel portion are both circular.
Another deflecting yoke core in the prior art is disclosed in Japanese Examined Patent Publication No. 1996-28194 and adopts a structure having a circular opening end at the neck portion and an oval opening end at the funnel portion. In addition, Japanese Unexamined Patent Publication No. 1995-37525 discloses a technology whereby the deflection efficiency is improved without compromising moldability, by forming the inner surface of the deflecting yoke core in an almost oval shape and forming the outer surface of the deflecting yoke core in an almost completely circular shape. Japanese Examined Patent Publication No. 1996-7781 also discloses a similar deflecting yoke core.
However, these prior art technologies, which do not take into consideration the relationship between the core sectional area and the density of the core internal magnetic flux distribution, present a concern in that the density of the core internal magnetic flux is not consistent, and magnetic saturation may occur over an area of the core where the density of the core internal magnetic flux is high, resulting in an image plane distortion.
These types of deflecting yoke cores are formed by molding ferrite powder or the like into a tube achieving a specific finished shape. The molded product may have dividing grooves formed in advance so that it can be divided into two core pieces along the dividing grooves so as to allow the horizontal deflection coil and the vertical deflection coil to be provided with ease.
As disclosed in Japanese Unexamined Patent Publication No. 1995-37525, Japanese Unexamined Utility Model Publication No. 1996-194, and U.S. Pat. No. 4,754,190, the dividing grooves in a deflecting yoke in the prior art are normally provided at two positions facing opposite each other over a horizontal axis.
However, the dividing grooves in this structure are provided at areas where the horizontal deflection magnetic field is the most intense. While the vertical deflection magnetic field has a low frequency of approximately 60 to 100 Hz, the horizontal deflection magnetic field has a high frequency of approximately 20 to 120 KHz, and thus, the horizontal deflection magnetic field may become a predominant cause of core loss. In addition, the presence of the dividing grooves provided at areas where the horizontal deflection magnetic field is the most intense, reduces the core sectional area of these areas and, as a result, the density of the magnetic flux attributable to the horizontal deflection magnetic field becomes extremely high, further increasing core loss. As is well known, core loss manifesting under these circumstances increases in proportion to the density of the magnetic flux to the power of 2 to 2.5. Thus, a problem arises in that the core temperature rises on the two positions facing opposite each other over the horizontal axis where the dividing grooves are provided.
In addition, if the opening end facing toward the funnel has a long diameter along a major axis and a short diameter along a minor axis, as disclosed in Japanese Examined Patent Publication No. 1996-28194 and Japanese Unexamined Patent Publication No. 1995-37525, the core density becomes lower near the minor axis due to the structure of the forming die. This results in a lower degree of core strength manifesting near the minor axis, and induces chipping of the core and the like.
Since there is an area with a low core density in the core as described above, the core shrinks unevenly during the baking process, resulting in a significant degree of deformation.
Clip grooves are formed at two sides of the dividing grooves in advance in an actual molded product. When forming a deflecting yoke by using such a deflecting yoke core, the deflecting yoke core is first divided into two pieces along the dividing grooves, after which a separator, a horizontal deflection coil and a vertical deflection coil are provided and then the divided core pieces are assembled. Subsequently, clips are provided at the clip grooves at the two sides of the dividing grooves to couple the two core pieces. This process tends to cause an increase in core temperature and chipping of the core or the like even more readily.
While the shape of the opening end at the funnel portion is either oval or rectangular, the shape of the opening end at the neck portion is circular in the prior art. Such a structure does not adequately support an in-line type cathode ray tube achieved by linearly providing three electron guns corresponding to the three primary colors.
Japanese Examined Patent Publication No. 1996-28194 discloses a deflecting yoke core adopting a slot structure, which is constituted by providing a plurality of projecting portions continuously and in a radial pattern along the inner surface of the core, extending from a neck portion to a funnel portion, and providing a horizontal deflection coil and a vertical deflection coil at grooves formed between the projecting portions. However, since the positions of the horizontal deflection coil and the vertical deflection coil are determined in conformance to the positions of the projecting portions, magnetic field distribution cannot be adjusted. Thus, a means other than the deflecting yoke must be employed to implement adjustment, such as a ballast operation distortion correction, a pincushion graphic distortion correction or a convergence characteristics correction.
As a means for solving the problem described above, Utility Model Registration No. 2580242 discloses a deflecting yoke core having coil guide grooves and projecting portions formed in a non-radial pattern, corresponding to the wiring pattern of a vertical deflection coil and a horizontal deflection coil designed in advance.
However, after the molding process, the deflecting yoke core disclosed in this Utility Model Registration cannot be rapped out along the direction of the core axis (tube axis), since projecting portions must be formed in a radial pattern relative to the core axis in order to allow the deflecting yoke core to be rapped out along the direction of the core axis.
When this type of deflecting yoke core is used to constitute a deflecting yoke, the core must achieve a high degree of dimensional accuracy, and the core and the cathode ray tube must be assembled with a high degree of accuracy to ensure that an electron beam is deflected as designed, because the electron beam is deflected along the inner surface of the deflecting yoke core. Since the core is mounted at the cathode ray tube via a separator, the core must be mounted at the separator with great accuracy in order to ensure that the core and the cathode ray tube are assembled with a high degree of accuracy.
However, since the deflecting yoke core is a baked product formed by baking a ferrite powder molding, it is bound to become deformed due to baking shrinkage. The rate of thermal contraction occurring at this time is fairly high at approximately 10% to 20%, resulting in a reduction of the volume of the baked core which is only approximately 60% of the volume of the unbaked core. Thus, the assembly accuracy with which the core and the cathode ray tube are assembled becomes poor, which prevents an electron beam from being accurately deflected as designed. Consequently, problems arise, such as a poor image quality attributable to misconvergence.
The problems attributable to the deformation of the baked core discussed above may be solved by grinding the core. However, it is difficult to grind the inner surface of the core if the shape of the opening end at the funnel portion is not circular. For this reason, the core inner surface is not ground, either at the funnel portion or at the neck portion, at a deflecting yoke core having the opening end at the funnel portion formed in a non-circular shape in the prior art. Thus, the problems attributable to baking deformation remain unsolved.
In addition, if the opening end at the funnel portion is formed in a non-circular shape as described above, there is no distinctive mark at the outer surface of the core that may be used as a positioning reference when mounting the core at the separator. For this reason, it is difficult to mount the deflecting yoke core at the separator accurately and thus, it is difficult to align the core axis of the deflecting yoke core with the tube axis of the cathode ray tube, presenting a limit to the extent to which assembly accuracy can be improved.
This problem may be eliminated by grinding the inner surface of the deflecting yoke core. Grinding methods that may be adopted for this purpose include a method disclosed in Japanese Unexamined Patent Publication No. 1989-319226 in which the neck portion is held from the inside and the outer surface is ground by using a rotating grindstone or the like. However, this prior art publication does not mention inner surface grinding in any way whatsoever.
Furthermore, a deflecting yoke core having an opening end at the funnel portion formed in a roughly rectangular shape cannot be ground with a rotating grindstone. Thus, it is difficult to align the core axis of the deflecting yoke core with the tube axis of the cathode ray tube when assembling such a deflecting yoke core and cathode ray tube, presenting a limit to the extent to which assembly accuracy can be improved.
Since the outer shape of the funnel portion at an opening end is normally circular, oval, roughly rectangular or the like, the outer surface continuous to the opening end of the funnel portion has a curved shape. For instance, Japanese Unexamined Patent Publication No. 1996-7781 discloses a core with an outer shape of the funnel portion at an opening end being roughly oval by combining a plurality of circular arcs with different radiuses.
Such a core does not have any distinctive mark at its outer surface to be used when positioning the deflecting yoke core relative to the cathode ray tube. For this reason, it is difficult to position the deflecting yoke core at the separator accurately and thus, it is difficult to align the core axis of the deflecting yoke core with the tube axis of the cathode ray tube, presenting a limit to the extent to which assembly accuracy can be improved.
It is necessary to hold the deflecting yoke core with a jig or the like when grinding the deflecting yoke core in order to improve deflection sensitivity as well as the accuracy with which the deflecting yoke core is positioned relative to the cathode ray tube. The deflecting yoke core may be held at the neck portion or at the opening end at the funnel portion. The neck portion, which has an almost consistent external diameter over a specific length along the core axis, can be used as a mechanical holding portion. However, the funnel portion is subject to the following restrictions when it is to be used as a mechanical holding portion.
Namely, there is a band-like portion constituted of a curved surface extending almost parallel to the core axis over the entire circumference of the opening end at the funnel portion, and this band-like portion may be used as a holding portion. The width of the band-like portion is usually 5 mm or smaller. If the outer shape of the funnel portion at an opening end is almost circular, a sufficient degree of mechanical holding strength can be assured even with a band-like portion having a width of 5 mm or smaller.
However, a core with an outer shape of the funnel portion at an opening end being rectangular cannot withstand the external force applied thereto during the machining process by using the band-like portion with a width of 5 mm or smaller as a holding portion, resulting in the core to fall, or a chip or crack or the like to occur. Ultimately, an area at the neck portion having an almost consistent external diameter over a specific length along the core axis must be used as a mechanical holding portion in this type of deflecting yoke core.
In such a situation, the correct selection of the length of the neck portion along the core axis which affects the core characteristics, the holding stability and the core volume, are crucial. For instance, in order to achieve a more lightweight core, the length of the neck portion which has an almost consistent external diameter along the core axis becomes excessively long when the core sectional area at the funnel portion is reduced, presenting a concern in that heat generation and magnetic saturation may occur.
If, on the other hand, no area achieving an almost consistent external diameter is provided at the neck portion or if such an area extends only over a very short distance, as shown in FIG. 1 of Japanese Unexamined Patent Publication No. 1995-37525 and in FIG. 2 of Japanese Unexamined Patent Publication No. 1996-7781, for instance, the deflecting yoke core cannot be held in a sufficiently stable manner during the machining process and thus, the deflecting yoke core cannot withstand the external force applied thereto during the machining process, resulting in the core to fall, or a chip or crack or the like to occur.
It is a first object of the present invention to provide a deflecting yoke core that optimizes the relationship between the core sectional area and the density of the core internal magnetic flux distribution and makes it possible to prevent magnetic saturation from occurring.
It is a second object of the present invention to provide a deflecting yoke core that makes it possible to minimize core loss and reduce the core temperature.
It is a third object of the present invention to provide a deflecting yoke core that eliminates the risk of core chipping.
It is a fourth object of the present invention to provide a deflecting yoke core that does not readily become deformed during the baking process.
It is a fifth object of the present invention to provide a deflecting yoke core that makes it possible to minimize core loss and reduce the core temperature.
It is a sixth object of the present invention to provide a deflecting yoke core that eliminates the risk of core chipping.
It is a seventh object of the present invention to provide a deflecting yoke core that does not readily become deformed during the baking process.
It is an eighth object of the present invention to provide a deflecting yoke core having a shape optimized for application in an in-line type cathode ray tube having three electron guns corresponding to the three primary colors, linearly provided.
It is a ninth object of the present invention to provide a deflecting yoke core that affords a high degree of freedom with regard to the positions of coils and makes it possible to improve deflection sensitivity, distortion characteristics, convergence characteristics and the like by adjusting the magnetic field distribution.
It is a tenth object of the present invention to provide a deflecting yoke core that can be rapped out with a high degree of reliability along the core axis.
It is an eleventh object of the present invention to provide a deflecting yoke core of which an opening end at the funnel portion is non-circular shaped, having a circular hole at an area toward the neck portion, and which achieves a high degree of dimensional accuracy.
It is a twelfth object of the present invention to provide a deflecting yoke core that can be positioned relative to a cathode ray tube with a high degree of accuracy, and a manufacturing method thereof.
It is a thirteenth object of the present invention to provide a deflecting yoke core that facilitates accurate positioning relative to a cathode ray tube.
It is a fourteenth object of the present invention to provide a deflecting yoke core that can be held in a stable manner during the machining process while maintaining a volume necessary to assure specific characteristics.
In order to achieve the first object described above, the deflecting yoke core according to the present invention to be mounted between a neck and a funnel of a cathode ray tube, has a hole extending from an opening end of a neck portion to an opening end of a funnel portion. The hole at the funnel portion widens toward the opening end of the funnel portion. An outer shape at the opening end of the funnel portion has a short diameter along a minor axis and a long diameter along a major axis. Core sectional areas along a plane parallel to and passing through a core axis are largest within an angular range of 30xc2x0 to 65xc2x0 measured around the core axis from a 0xc2x0 reference angle at the minor axis.
Research conducted by the inventors of the present invention has revealed that when a deflecting yoke is constituted by providing a horizontal deflection coil and a vertical deflection coil at a deflecting yoke core, and a vertical deflection magnetic field and a horizontal deflection magnetic field are created by the individual coils, the resulting magnetic flux does not achieve consistency in the core.
In more specific terms, the highest degree of core internal magnetic flux density is achieved within an angular range of 30xc2x0 to 65xc2x0 measured around the core axis from a 0xc2x0 reference angle at a position at which the density of the core internal magnetic flux attributable to the horizontal deflection magnetic field is the lowest, when the density of the core internal magnetic flux is measured at various sectional planes parallel to and passing through the core axis, with an opening end at the neck portion and the opening end at the funnel portion both formed in a circular shape, in the prior art.
Accordingly, it is ensured in the deflecting yoke core according to the present invention that the core sectional areas along a plane parallel to and passing through a core axis are largest within an angular range of 30xc2x0 to 65xc2x0 measured around the core axis from a 0xc2x0 reference angle at the minor axis.
Thus, consistency is achieved with regard to the density of the core internal magnetic flux over the entire core, thereby preventing local magnetic saturation. If the core assumes a shape achieving the largest core sectional area outside the angular range of 30xc2x0 to 65xc2x0, magnetic saturation may occur over the angular range of 30xc2x0 to 65xc2x0 in which the density of the core internal magnetic flux is high. While magnetic saturation can be prevented by increasing the core sectional area over the entire core, the resulting core is bound to have an inefficient shape.
Another means for achieving the first object, i.e., prevention of magnetic saturation, is provided by ensuring that the core density at core sectional areas along a plane parallel to and passing through a core axis is largest within an angular range of 30xc2x0 to 65xc2x0 measured around the core axis from a 0xc2x0 reference angle at the minor axis.
Through this means, local magnetic saturation over the angular range of 30xc2x0 to 65xc2x0, in which the density of the core internal magnetic flux is the highest, can be prevented. If the core assumes a shape in which the core density is the highest at a core section outside the angular range of 30xc2x0 to 65xc2x0, magnetic saturation may occur over the angular range of 30xc2x0 to 65xc2x0 in which the density of the core internal magnetic flux is high. If, on the other hand, the core sectional area is increased for the entire core, the core is bound to have an inefficient shape.
In order to achieve the second object mentioned earlier, the deflecting yoke core according to the present invention to be mounted between a neck and a funnel of a cathode ray tube, has a hole extending from an opening end of a neck portion to an opening end of a funnel portion. The hole at the funnel portion widens toward the opening end of the funnel portion. An outer shape at the opening end of the funnel portion has a short diameter along a minor axis and a long diameter along a major axis. The deflecting yoke core is further provided with dividing grooves extending along the core axis at a core surface near the minor axis.
In an application in a deflecting yoke, a horizontal deflection coil and a vertical deflection coil are provided so as to set the position of the minor axis in correspondence to a position at which the density of the magnetic flux attributable to the horizontal deflection magnetic field, is the lowest. With this structure, having dividing grooves provided at the position at which the density of the magnetic flux attributable to the horizontal deflection magnetic field is the lowest, the density of the magnetic flux attributable to the horizontal deflection magnetic field is least affected by the dividing grooves, and reductions in core loss and heat generated at the core are thus achieved.
It is desirable to form the dividing grooves in a linear shape and to allow the dividing grooves to open at an opening end edge at the neck portion. Such a structure allows the core, which is constituted by molding magnetic powder such as ferrite powder or magnetic metal powder, to be rapped out smoothly.
In another desirable mode, dividing grooves are provided at positions facing opposite each other at an outer circumferential surface and an inner circumferential surface. By adopting this structure, it becomes possible to divide the core constituted of a ferrite molding with ease.
The dividing grooves formed at the outer circumferential surface and the dividing grooves formed at the inner circumferential surface are continuous to each other at the opening end edge at the neck portion. This structure allows the core to be divided with ease. The dividing grooves should preferably be V-shaped, since a V-shape effectively allows the core to be divided into two pieces with ease.
In order to achieve the third and fourth objects mentioned earlier, the deflecting yoke core according to the present invention is formed as a tube to be mounted between a neck and a funnel of a cathode ray tube, and has an outer circumferential surface. The outer circumferential surface at a funnel portion widens toward an opening end of the funnel portion. An outer shape at the opening end of the funnel portion has a short diameter along a minor axis and a long diameter along a major axis. At least one first indented portion is provided at the outer circumferential surface near the minor axis.
Research conducted by the inventors of the present invention has revealed that when the outer shape of the funnel portion at an opening end has a short diameter along a minor axis and a long diameter along a major axis, the core density is lower near the minor axis.
Accordingly, the first indented portion is provided at the outer circumferential surface of the deflecting yoke core according to the present invention. During the pressurized molding process implemented by using magnetic powder such as ferrite powder, the magnetic powder can be pressurized with a projecting portion provided at the molding die in correspondence to the first indented portion. As a result, the core density around the first indented portion corresponding to the projecting portion can be increased.
In addition, since the first indented portion is located at the outer circumferential surface near the minor axis, the core density ultimately increases near the minor axis. Thus, the core strength improves near the minor axis, so that core chipping is prevented.
Furthermore, since the core density increases near the minor axis, as described above, a more uniform core density distribution is achieved. As a result, the deflecting yoke core according to the present invention shrinks in an even manner and does not become deformed readily during the baking process.
In order to achieve the fifth, sixth and seventh objects mentioned earlier, the deflecting yoke core according to the present invention to be mounted between a neck and a funnel of a cathode ray tube, has a hole extending from an opening end of a neck portion to an opening end of a funnel portion. The hole at the funnel portion widens toward the opening end of the funnel portion. An outer shape at the opening end of the funnel portion has a short diameter along a minor axis and a long diameter along a major axis. The deflecting yoke core according to the present invention is provided with dividing grooves extending along a core axis at a core surface near the minor axis, and clip grooves are provided at the outer circumferential surface at two ends of the minor axis.
In an application in a deflecting yoke, a horizontal deflection coil and a vertical deflection coil are provided so as to set the position of the minor axis in correspondence to a position at which the density of the magnetic flux attributable to the horizontal deflection magnetic field is the lowest. In this structure, having dividing grooves provided at the positions at which the density of the magnetic flux attributable to the horizontal deflection magnetic field is the lowest, the density of the magnetic flux attributable to the horizontal deflection magnetic field is least affected by the dividing grooves, to achieve reductions in core loss and heat generated at the core.
Research conducted by the inventors of the present invention has revealed that when the outer shape of the funnel portion at an opening end has a short diameter along a minor axis and a long diameter along a major axis, the core density is lower near the minor axis.
Accordingly, the clip grooves are formed at the outer circumferential surface of the deflecting yoke core according to the present invention. During the pressurized molding process implemented by using magnetic powder such as ferrite powder, the magnetic powder can be pressurized with projecting portions provided in correspondence to the clip grooves. As a result, the core density around the clip grooves corresponding to the projecting portions can be increased.
In addition, since the clip grooves are located at the outer circumferential surface on the two ends of the minor axis, the core density ultimately increases near the minor axis. Thus, the core strength improves near the minor axis, so that core chipping is prevented.
Furthermore, since the core density increases near the minor axis, as described above, a more uniform core density distribution is achieved. As a result, the deflecting yoke core according to the present invention shrinks in an even manner and does not become deformed readily during the baking process.
In order to achieve the eighth object mentioned earlier, the deflecting yoke core according to the present invention to be mounted between a neck and a funnel of a cathode ray tube, has a hole extending from an opening end of a neck portion to an opening end of a funnel portion. The hole at the funnel portion widens toward the opening end of the funnel portion. The hole at the opening end of the funnel portion is curved along an entire circumference, and the hole at both the funnel portion and the neck portion has a short diameter along a minor axis and a long diameter along a major axis.
Since the deflecting yoke core has a hole having a short diameter along a minor axis and a long diameter along a major axis at the neck portion as well as at the funnel portion, the neck portion, too achieves a shape suitable for application in an in-line type cathode ray tube having three linearly positioned electron guns in correspondence to the three primary colors. Thus, a deflecting yoke core achieving an optimal shape for application in an in-line type cathode ray tube is provided.
In order to achieve the ninth and tenth objects, the deflecting yoke core according to the present invention is formed as a tube to be mounted between a neck and a funnel of a cathode ray tube and has a plurality of projecting portions provided in a radial pattern along an inner surface from a neck portion toward a funnel portion, with a plurality of grooves formed between the plurality of projecting portions.
The projecting portions are provided separately at the neck portion and the funnel portion, and each include a surface that faces opposite the core axis and inclines over an increasingly greater distance from the core axis viewed along a direction extending from the neck portion toward the funnel portion.
As described above, since a plurality of projecting portions are provided in a radial pattern along the inner surface from the neck portion to the funnel portion and a plurality of grooves are formed between the projecting portions, windings of the deflection coils are prevented from becoming misaligned at the bottom surfaces of the grooves between the projecting portions.
In addition, since the projecting portions are provided separately at the neck portion and the funnel portion, the winding distribution can be adjusted in, for instance, a radial pattern and a non-radial pattern, to facilitate correction of distortion or misconvergence manifesting after the deflecting yoke is assembled.
Furthermore, since the plurality of projecting portions are provided in a radial pattern along the inner surface and their surfaces facing opposite the core axis incline over increasingly greater distances from the core axis when viewed along the direction extending from the neck portion to the funnel portion, the deflecting yoke core constituted by molding magnetic powder such as ferrite powder can be easily rapped out with a high degree of reliability along the direction in which the core axis (tube axis) extends after it is molded.
In order to achieve the eleventh and twelfth objects mentioned earlier, the deflecting yoke core according to the present invention to be mounted between a neck and a funnel of a cathode ray tube, has a hole extending from an opening end of a neck portion to an opening end of a funnel portion. The hole at the funnel portion widens toward the opening end of the funnel portion. The hole at the funnel portion has a short diameter along a minor axis and a long diameter along a major axis. The hole at the neck portion has a circular shape and a ground inner surface.
Since the inner surface of the hole at the neck portion is ground in the deflecting yoke core with the hole at the funnel portion formed in a non-circular shape and the hole in the neck portion formed in a circular shape, the dimensional accuracy at the neck portion is improved. This, in turn, ensures a high degree of assembly accuracy when mounting a deflecting yoke constituted by using the deflecting yoke core, at a cathode ray tube. The hole at the neck portion is formed in a circular shape and can be ground with ease by employing, for instance, a rotary grinder.
With the dimensional accuracy of the hole at the neck portion improved as described above, the core axis, i.e., the central axis of the hole, can be set with a high degree of accuracy, which, in turn, makes it possible to surface-grind the outer surface of the funnel portion relative to the core axis and then to use the flat surface obtained through grinding as a positioning reference when positioning the core relative to the separator. Thus, the core is positioned relative to a separator with a high degree of accuracy and, ultimately, the deflecting yoke core can be positioned with a high degree of accuracy relative to the cathode ray tube.
Another deflecting yoke core according to the present invention to be mounted between a neck and a funnel of a cathode ray tube, has a hole extending from an opening end of a neck portion to an opening end of a funnel portion. The hole at the funnel portion widens toward the opening end of the funnel portion. The hole at least at the funnel portion has a short diameter along a minor axis and a long diameter along a major axis and a ground inner surface.
Since the deflecting yoke core has a hole at a funnel portion widening toward an opening end of the funnel portion with the hole at the funnel portion having a short diameter along a minor axis and a long diameter along a major axis, the core can be utilized in a cathode ray tube for a color television image receiver having a wide display panel.
In addition, since the inner surface of the hole is ground at the funnel portion, the dimensional accuracy of the core at the funnel portion is improved to achieve better assembly accuracy when mounting the deflecting yoke core at a cathode ray tube.
In a desirable mode, the inner surface of the hole may be ground at the neck portion as well, so that the assembly accuracy with which the deflecting yoke core is mounted at the cathode ray tube is further improved by assuring a higher degree of dimensional accuracy at the neck portion as well as at the funnel portion.
In order to achieve the thirteenth object mentioned earlier, the deflecting yoke core according to the present invention is formed as a tube to be mounted between a neck and a funnel of a cathode ray tube, and has an outer shape. The outer shape at a funnel portion widens toward an opening end of the funnel portion. The outer shape at the opening end of the funnel portion has a short diameter along a minor axis and a long diameter along a major axis and includes at least one ground flat surface at an outer circumferential surface at the opening end of the funnel portion.
As described above, the deflecting yoke core has an outer shape at a funnel portion widening toward an opening end of the funnel portion, with the outer shape at the opening end of the funnel portion having a short diameter along a minor axis and a long diameter along a major axis. This structure improves the deflection efficiency when adopted in conjunction with a cathode ray tube for a color television image receiver with a wide display panel.
In addition, there is at least one ground flat surface at the outer circumferential surface toward the opening end of the funnel portion. The ground flat surface extends parallel to the core axis. This structure facilitates alignment of the core axis with the tube axis of the cathode ray tube by allowing the ground flat surface to be used as a reference surface. Thus, accurate positioning of the core relative to the cathode ray tube is facilitated.
Japanese Unexamined Patent Publication No. 1989-319226 discloses a means for grinding the outer surface of a deflecting yoke core, through which the neck portion is held from the inside and the outer surface is ground by using a rotary grindstone or the like. However, the grinding process is implemented to improve the dimensional accuracy of the outer surface in this prior art technology rather than to achieve accurate positioning of the core relative to the cathode ray tube.
In a desirable mode, two or more ground flat surfaces may be provided, with two consecutive surfaces set over angular intervals of approximately 90xc2x0 or approximately 180xc2x0, to realize even more reliable alignment of the core with the cathode ray tube with the plurality of reference surfaces.
In order to achieve the fourteenth object described above, the deflecting yoke core according to the present invention is formed as a tube to be mounted between a neck and a funnel of a cathode ray tube. An outer shape at an opening end of a funnel portion has a short diameter along a minor axis and a long diameter along a major axis. In addition, 5 mmxe2x89xa6Bxe2x89xa6A/2 mm is satisfied, with A representing an entire length of the core along the core axis which is the sum of a length B of the neck portion along the core axis and a length of the funnel portion along the core axis.
According to the present invention, the neck portion refers to an area positioned toward the neck of the cathode ray tube, over which the external diameter essentially remains constant. The funnel portion refers to the remaining portion of the core excluding the neck portion. The length along the core axis refers to the length of the deflecting yoke core formed in a tubular shape, which is measured along the core axis.
The neck portion is utilized as a holding portion when machining the inner surface and the like of the deflecting yoke core. If the length B of the neck portion along the core axis is less than 5 mm (B less than 5 mm), the neck portion cannot be fully held by the processing machine and the force with which the neck portion is held may not be large enough to withstand the force of the machine performing the process or to withstand the weight of the deflecting yoke core resulting in a chip or crack to occur.
If, on the other hand, the length B of the neck portion along the core axis is equal to or larger than 5 mm (Bxe2x89xa75 mm), the neck portion can be held by the processing machine in a fully stable manner. Thus, a sufficient degree of holding force to withstand the mechanical working force imparted while abrading the core inner surface and the like and to withstand the weight of the deflecting yoke core is assured to prevent the core from falling, or a chip or crack or the like from occurring. As a result, the inner surface and the like of the deflecting yoke core can be machined with a high degree of accuracy and stability to improve the positioning accuracy when the deflecting yoke core is mounted at the cathode ray tube, so that, ultimately, a deflecting yoke capable of accurately controlling the electron beams in the cathode ray tube and achieving a high degree of deflection sensitivity is obtained. Problems of heat generation and magnetic saturation do not arise as long as the length B of the neck portion along the core axis is equal to or larger than 5 mm and equal to or smaller than (A/2) mm.
Once the length B of the neck portion along the core axis exceeds (A/2) mm, the sectional area of the funnel portion becomes small and, as a result, problems of heat generation and magnetic saturation may arise.